Partially Logged Rainforests May Emit More Carbon than Thought

It is well known that tropical deforestation is just as costly as carbon pollution when it comes to greenhouse gas emissions. But while research has mostly focused on forests that have been completely mowed down, scientists are now saying that partially logged forests play just as crucial a role, and may emit more carbon than previously thought.

That's at least according to a new study published in the journal Environmental Research Letters, which details how global carbon emissions from forests could have been underestimated because calculations have not fully accounted for the dead wood from logging.

Living trees, via photosynthesis, take in carbon dioxide (CO2) whereas dead and decaying ones release it. Understanding the balance is important in order for scientists to determine whether a large area of forest is a source of CO2, or a "sink" that helps to absorb the greenhouse gas from the atmosphere.

Astonishingly, forestry, agriculture and land-use changes account for nearly 25 percent of global greenhouse gas emission - that's second only to the energy sector. And if that wasn't bad enough, now new research led by Imperial College London (ICL) finds that partially-logged rainforests are probably emitting more carbon than we assumed because of the large amount of dead wood they contain.

In fact, dead wood comprises up to 64 percent of the biomass found in these tropical forests; whereas in untouched forests, dead wood makes up less than 20 percent of the total aboveground biomass. (Scroll to read on...)

That was determined after researchers surveyed a large area in the Stability of Altered Forest Ecosystems (SAFE) site - a region of rainforest in Malaysian Borneo. They assessed the deadwood contributions across a "disturbance gradient" - a range of landscapes including pristine forest, logged forests of increasing severity, and oil palm plantation.

Until now, when estimating carbon emissions from logged rainforests, researchers had assumed that when live trees are cut down and moved out of the forest, the amount of dead wood is significantly reduced. However, that does not seem to be the case.

According to the new findings, because selective logging leaves behind significant damage and tree debris, dead wood actually accounts for a large part of the total aboveground biomass. This means that all this time scientists have drastically underestimated the role these forests play in the greenhouse gas problem and climate change.

"I was surprised by how much of the biomass dead wood accounted for in badly logged forests," lead author Dr. Marion Pfeifer said in a statement. "That such logged forests are not properly accounted for in carbon calculations is a significant factor. It means that a large proportion of forests worldwide are less of a sink and more of a source, especially immediately following logging, as carbon dioxide is released from the dead wood during decomposition."

"Selectively-logged tropical forests now make up about 30 percent of rainforests worldwide. This means such global calculations are wrong at least 30 percent of the time," Pfeifer added.

The hope is that we can completely end deforestation by the year 2030, but until then researchers now can better understand how logging of rainforests, even partial logging, impacts carbon emissions worldwide.

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